Subject: Re: [PATCH V2] CAN: Add Flexcan CAN controller driver

From: Oliver Hartkopp <[email-masked]>
Date: Tue, 28 Jul 2009 15:21:40 +0200

Sascha Hauer wrote:
> Hi,
> 
> Here is the second version of the flexcan driver.

Hi Sascha,

some more points i forgot to mention, sorry ...

> +/* Structure of the message buffer */
> +struct flexcan_mb {
> +	u32	can_dlc;
> +	u32	can_id;
> +	u32	data[2];
> +};

This looks really hackish and does not reflect the structure of a flexcan
message buffer! The data is 'u8' and the name of 'dlc' for the
description/flag register is bad.

> +
> +static int flexcan_start_xmit(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct can_frame *frame = (struct can_frame *)skb->data;
> +	struct flexcan_priv *priv = netdev_priv(dev);
> +	struct flexcan_regs __iomem *regs = priv->base;

> +	u32 can_id;
> +	u32 dlc = MB_CNT_CODE(0xc) | (frame->can_dlc << 16);

Naming this variable 'dlc' does not hit the point. See below.

> +	u32 *can_data;

Really this needs to be fixed up by defining a proper mailbox struct.

> +
> +	netif_stop_queue(dev);
> +
> +	if (frame->can_id & CAN_EFF_FLAG) {
> +		can_id = frame->can_id & MB_ID_EXT;

Please use CAN_EFF_MASK here.

> +		dlc |= MB_CNT_IDE | MB_CNT_SRR;
> +	} else {
> +		can_id = (frame->can_id & CAN_SFF_MASK) << 18;
> +	}

Just nitpicking for Kernel coding style:
remove the last '{' and '}' pair.

> +
> +	if (frame->can_id & CAN_RTR_FLAG)
> +		dlc |= MB_CNT_RTR;
> +
> +	writel(dlc, &regs->cantxfg[TX_BUF_ID].can_dlc);
> +	writel(can_id, &regs->cantxfg[TX_BUF_ID].can_id);
> +
> +	can_data = (u32 *)frame->data;
> +	writel(cpu_to_be32(*can_data), &regs->cantxfg[TX_BUF_ID].data[0]);
> +	writel(cpu_to_be32(*(can_data + 1)), &regs->cantxfg[TX_BUF_ID].data[1]);

IMHO it is not really transparent, that this is a correct handling to copy the
  can_frame.data[] on all architectures. I bet creating a for-statement
regarding the dlc is not slower and makes really clear, what's going on here.

> +
> +	writel(dlc, &regs->cantxfg[TX_BUF_ID].can_dlc);
> +
> +	kfree_skb(skb);
> +
> +	return NETDEV_TX_OK;
> +}
> +
> +static void flexcan_rx_frame(struct net_device *ndev,
> +		struct flexcan_mb __iomem *mb)
> +{
> +	struct net_device_stats *stats = &ndev->stats;
> +	struct sk_buff *skb;
> +	struct can_frame *frame;
> +	int ctrl = readl(&mb->can_dlc);

'ctrl' is much better than 'dlc' naming above :-)

> +	int length = (ctrl >> 16) & 0x0f;

is probably not enough ... use %9 or an additional check.

> +	u32 id;
> +
> +	skb = dev_alloc_skb(sizeof(struct can_frame));
> +	if (!skb) {
> +		stats->rx_dropped++;
> +		return;
> +	}
> +
> +	frame = (struct can_frame *)skb_put(skb,
> +			sizeof(struct can_frame));
> +
> +	frame->can_dlc = length;
> +	id = readl(&mb->can_id) & MB_ID_EXT;

like above use CAN_EFF_MASK

or at least rename MB_ID_EXT to MB_ID_EXT_MASK

> +
> +	if (ctrl & MB_CNT_IDE) {
> +		frame->can_id = id & CAN_EFF_MASK;
> +		frame->can_id |= CAN_EFF_FLAG;
> +		if (ctrl & MB_CNT_RTR)
> +			frame->can_id |= CAN_RTR_FLAG;
> +	} else {
> +		frame->can_id  = id >> 18;
> +		if (ctrl & MB_CNT_RTR)
> +			frame->can_id |= CAN_RTR_FLAG;
> +	}
> +
> +	*(u32 *)frame->data = be32_to_cpu(readl(&mb->data[0]));
> +	*((u32 *)frame->data + 1) = be32_to_cpu(readl(&mb->data[1]));

Same as above.

Please write readable an maintainable code and let the compiler do his job.

Thanks,
Oliver